1. Field of the Invention
The present invention relates to a digital television, and more particularly, to a device and method for symbol clock recovery in a digital television. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for enabling the symbol clock recovery to be more accurately performed.
2. Discussion of the Related Art
An advanced television systems committee (ATSC) 8 VSB (Vestigial Side Band) transmission system proposed by most current digital transmission systems and a US directed digital TV transmission mode loads data only in a transmission signal to increase an efficiency of a frequency. That is, clock information needed for data recovery at a receiving party is not transmitted. Therefore, the same clock as that employed during the transmission should be generated among the received signals to recover the data. A symbol clock recovery device performs the role.
FIG. 1 is a block diagram illustrating a general digital TV receiver having such symbol clock recovery. Referring to FIG. 1, if a radio frequency (RF) signal modulated in a VSB mode is received through an antenna 101, a tuner 102 selects a desired channel frequency. Then, the tuner 102 converts a VSB signal of an RF band to a first intermediate frequency (IF) band, and outputs to an analog processor 103. The analog processor 103 performs passband filtering and gain controlling to the first IF signal outputted from the tuner 102 for converting the first IF signal into a second IF signal, and outputs to an A/D (analog-to-digital) converter 104. The A/D converter 104 digitalizes the second IF signal and outputs the digitalized second IF signal to a phase splitter 105.
The phase splitter 105 splits (or separates) the digital signal into passband real/imaginary signals, the phases of which form an angle of −90°. The passband real/imaginary signals are then outputted to a carrier recovery 106. Hereinafter, the passband real signal will referred to as I, and the passband imaginary signal will be referred to as Q, which are both outputted from the phase splitter 105, for simplicity. The carrier recovery 106 converts I and Q passband signals to I and Q baseband signals, which are then outputted to a symbol clock recovery 107 for recovering the symbol clocks. Then, the data passed through the symbol clock recovery 107 are inputted to a channel equalizer 108.
The channel equalizer 108 removes linear noise existing on a transmission channel from the signal having the carrier recovered, and then outputs the signal to a phase tracker 109. However, the carrier recovery 106 cannot completely recover the phase of the carrier. Accordingly, in order to compensate the incomplete phase error, the output of channel equalizer 108 is passed through the phase tracker 109. The output of the phase tracker 109 is inputted to a forward error correction (FEC) unit 110, thereby correcting errors in digital codes received from a digital transmission through t channel decoder.
In other words, a transmitter such as a broadcast station selects an adequate method so as to transmit a transmission signal by channel encoding. Then, a receiver such as a digital television (TV) decodes the transmission signal, so as to correct the errors generated while passing though the channel. Herein, the forward error correction (FEC) unit 110 is the block carrying out the decoding process. The signal passing through the FEC unit 110 is inputted to an A/V signal processing unit 111. Then, the A/V signal processing unit 111 recovers audio and video signals compressed in MPEG-2 and Dolby AC-2 methods back to their initial forms.
However, as shown in FIG. 1, the symbol clock recovery 107 is located behind the carrier recovery 106. Thus, the symbol clock recovery 107 is influenced by the carrier recovery 106. Therefore, if the carrier recovery 106 is unable to recover a carrier frequency and phase due to multiple channel interference, the symbol clock recovery 107 is also unable to recover symbol clock. More specifically, in a structure having the carrier recovery and the symbol clock recovery sequentially connected to one another, the performance of the carrier recovery greatly influences the performance of the symbol clock recovery. In other words, in a structure whereby the carrier recovery and the symbol clock recovery are sequentially connected, the function and performance of the carrier recovery largely influence the function and performance of the symbol clock recovery. Thus, the symbol clock recovery is affected by the remained frequency and phase difference caused from the carrier recovery, thereby resulting in a deficient performance of the symbol clock recovery.